The present invention relates to a shape measuring apparatus for measuring a shape by use of a probe or the like, wherein a probe that specifies the surface in XY-axis directions or a measured object is moved in the XY-axis directions on a stage, and a shape of the measured object is measured by the probe.
With the recent advancement of the optical electronics technology, demands are increasing for improvement in picture quality in cameras such as digital cameras and mobile devices using cameras such as smartphones. Especially, demands are increasing for high-accuracy lenses which are finished with an error of 0.1 μm (100 nm) or less with respect to designed shapes, as surface shapes of lenses for use in the cameras. Among those, also in a shape measuring apparatus which performs high-accuracy measurement, demands are further increasing for high accuracy due to reduction in noise at the time of measurement. Above all, in the shape measuring apparatus where a probe is scanned to measure a shape, it has been required to reduce vibration noise at the time of scanning measurement, and performance of an XY stage has a higher proportion of an effect in reducing vibrations at the time of scanning.
Among stage structures for use in conventional shape measuring apparatuses and the like, there is a stage structure where a portion at the end of a linear motor which receives driving force of the linear motor is supported by another support member different from a movable section and a fixed section of the stage, to prevent the whole stage from receiving a counteraction of force at the time of driving the stage, thus reducing vibrations generated in the shape measuring apparatus (Japanese Unexamined Patent Publication No. 5-77126).
FIGS. 8A and 8B show a conventional stage structure described in Japanese Unexamined Patent Publication No. 5-77126.
In FIGS. 8A and 8B, numeral 101 denotes a surface plate, numeral 102 denotes a movable stage, numeral 103X denotes a first X-axial linear motor, numeral 103Y denotes a first Y-axial linear motor, numeral 104X denotes a second X-axial linear motor, numeral 104Y denotes a second Y-axial linear motor, numeral 105X denotes a support plate which supports the second X-axial linear motor 104X, and numeral 105Y denotes a support plate which supports the second Y-axial linear motor 104Y. The support plates 105X, 105Y are mounted on a floor 109 different from the surface plate 101. Further, the surface plate 101 is configured such that vibrations are isolated by a vibration isolator 110. Moreover, the support plates 105X, 105Y which support the second X-axial/Y-axial linear motors 104X, 104Y are configured so as to be supported by extension of arms from the floor 109.
The movable stage 102 is supported so as to be positioned movably in XY directions by use of an air bearing or the like at a point of intersection between an X-axis yoke 106X, which moves in the Y direction and controls an X-axial moving direction, and a Y-axis yoke 106Y, which moves in the X direction and controls a Y-axial moving direction. With this configuration, the X-axis yoke 106X moves in the Y-direction by thrust of the second Y-axial linear motor 104Y, to roughly position the movable stage 102 in the Y-direction. By a similar procedure, the Y-axis yoke 106Y moves in the X-direction by thrust of the second X-axial linear motor 104X, to roughly position the movable stage 102 in the X-direction.
Here, in a guide of the X-axis yoke 106X moving in the Y-direction, a moving direction is defined by a Y-axis air bearing 107Y, and in a guide of the Y-axis yoke 106Y moving in the X-direction, a moving direction is defined by an X-axis air bearing 107X.
Further, it is configured that thrust is generated against the movable stage 102 in the X-direction and the Y-direction respectively by a coil 108X for driving in the X-direction and a coil 108Y for driving in the Y-direction to perform fine positioning, the coil 108X and the coil 108Y being respectively mounted in the X-axis yoke 106X and the Y-axis yoke 106Y.
In FIGS. 8A and 8E, a conventional example of driving the movable stage 102 in the Y-axis direction will be described hereinafter, where high-speed, rough positioning is performed by large thrust by use of the second Y-axial linear motor 104Y. At this time, the support plate 105Y of the second Y-axial linear motor 104Y is supported by extension of the arm from the floor 109. For this reason, at the time of driving the second Y-axial linear motor 104Y, counteracting force is generated on the fixed side of the second Y-axial linear motor 104Y against force generated by the X-axis yoke 106X to drive the movable stage 102. This counteracting force is not transmitted to the surface plate 101 constituting a stage unit. Hence the surface plate 101 does not generate vibrations and the like in high-speed, rough positioning with large thrust by the second Y-axial linear motor 104Y.